The present invention pertains to reversible reciprocating piston machines, and particularly to reversible hermetic reciprocating piston compressors. More specifically, the present invention relates to compressors including an eccentric cam operably engaged with a crankpin and connecting rod to provide a first piston stroke in a first direction of crankshaft rotation and a second piston stroke in a second direction of crankshaft rotation.
Reciprocating piston compressors, such as the compressor disclosed in U.S. Pat. No. 5,281,110, which is assigned to the present assignee, the disclosure of which is incorporated herein by reference, are generally of fixed displacement and powered by an electric motor which rotates in a single direction. Also known in the art are reversible hermetic reciprocating piston compressors in which a piston has a first stroke length when driven by a crankshaft rotating in a first, forward direction, and a second stroke length when driven by the crankshaft rotating in a second, reverse direction. Two separate stroke lengths are achieved through use of an eccentric cam which rotates relative to the crankshaft between stops thereon corresponding to first and second angular cam positions which, in turn, correspond to the first and second stroke lengths. These reversible compressors provide the advantage of having one displacement when the crankshaft is rotated in the forward direction, and another displacement when the crankshaft is rotated in the reverse direction. Typical variable stroke, reversible drive compressors, however, do not provide means for positively maintaining engagement between the cam stop and the crankshaft corresponding to the greater stroke length during rotation of the crankshaft without a latching mechanism which holds the cam and crankshaft in engagement during rotation in one of these two directions. If the cam and crankshaft are not continually maintained in engagement during crankshaft rotation, the reexpansion of gas in the cylinder after the piston reaches top-dead-center (TDC) may force the piston away from its TDC position at such a speed that the cam may rotate relative to the crankshaft, separating the cam and crankshaft stops. The separation of these stops result in their subsequently slamming together as the rotating crankshaft catches up to the cam, causing considerable component stresses, adversely affecting durability, and producing undesirable noise.
To prevent this undesirable loss of contact between the crank and the cam a reversible reciprocating compressor was adapted with a centrifugally activated latching mechanism which coupled the crank with the cam when the crank was rotating in the forward direction. The disclosure of a reversible reciprocating compressor employing a latching mechanism is provided in U.S. Pat. No. 5,951,261 to Paczuski and U.S. Pat. No. 6,190,137 to Robbins et al., both of which are assigned to the assignee of the present application, the disclosures of which are expressly incorporated herein by reference. Although effective in maintaining contact between the cam and crankshaft, implementing the latching mechanism requires multiple parts and additional machining at a significant additional cost.
U.S. Pat. No. 6,132,177 to Loprete et al. discloses a reversible reciprocating compressor having a flyweight incorporated into the cam assembly exerting a centrifugal force which is transmitted to the crankshaft from the cam assembly to prevent separation of the cam and crankshaft. The flyweight is located opposite the engagement between the cam assembly and the crankshaft. As the rotational speed of the crankshaft increases, the flyweight imparts a force influencing the cam assembly and crankshaft into engagement. However, since the centrifugal force is effective after the crankshaft has gained significant rotation, the flyweight has significantly less effect at low crankshaft speeds, i.e., at start-up. As a result, undesirable noise and damage due to impact may occur during insignificant crankshaft speeds.
What is needed is a reversible compressor assembly which is simple in construction and is adapted to avoid undesirable impact between the cam and crankshaft at any crankshaft speed and in either direction. Further, a reversible compressor which significantly reduces wear or other damage of the contacting surfaces defined by the crankshaft and the cam assembly, is desirable.
The present invention overcomes the disadvantages of prior reversible compressor assemblies by providing a reversible, variable stroke compressor assembly including a crankshaft having a drive portion coacting with a driven portion of a cam assembly through lubricated sliding engagement and disengagement between the contacting surfaces to reduce impact, noise and damage.
The present invention provides a reversible reciprocating piston compressor including a crankcase defining at least one cylinder therein, and a crankshaft which rotates in opposite, forward and reverse directions and is rotatably supported by the crankcase. The crankshaft includes a drive portion and a crankpin eccentrically positioned relative to an axis of rotation of the crankshaft. A piston is reciprocable within the cylinder and a connecting rod assembly is provided between the crankpin and the piston to reciprocally drive the piston in response to forward or reverse rotation of the crankshaft. A cam assembly is operably connected to the crankpin and is engageable with the drive member to effectuate a first stroke length in a first direction of rotation of the crankshaft, and a second stroke in a second direction of rotation of the crankshaft. The cam assembly includes a cam, a driven portion and a counterweight. The cam is interposed between the connecting rod assembly and the crankpin. The driven portion is attached to the cam and is in a contacting relationship with the crankshaft drive portion through at least one contact interface. The contact interface is oriented at a non-zero angle to a radial reference originating from a centerline axis of the crankpin. The counterweight is attached to the cam and has a center of mass located radially adjacent to or through the contact interface. The drive portion is engageable and disengageable with the driven portion through sliding movement of the drive portion relative to the driven portion along the contact interface.
The present invention further provides a reversible reciprocating piston compressor including a counterweight attached to the cam and being structured and arranged to provide an inertial force directed through a center of mass of the cam. The center of mass of the cam is located radially adjacent or through the contact interface. The driven portion and the drive portion resist separation under the influence of the inertial force.
The present invention further provides a reversible reciprocating piston compressor having a counterweight attached to the cam being structured and arranged to provide a centrifugal force on the cam assembly when the crankshaft has attained a running speed. The centrifugal force urges a reduction in a force of contact exerted by the drive portion on the driven portion to thereby retain a film of lubricating oil between the drive and driven portions.
The present invention further provides a reversible reciprocating piston compressor including a crankcase defining at least one cylinder therein, and a crankshaft which rotates in opposite, forward and reverse directions and is rotatably supported by the crankcase. The crankshaft includes a drive portion and a crankpin eccentrically positioned relative to an axis of rotation of the crankshaft. A piston is reciprocable within the cylinder and a connecting rod assembly is provided between the crankpin and the piston to reciprocally drive the piston in response to forward or reverse rotation of the crankshaft. A cam assembly is operably connected to the crankpin and is engageable with the drive member to effectuate a first stroke length in a first direction of rotation of the crankshaft, and a second stroke in a second direction of rotation of the crankshaft. The cam assembly includes a cam and a driven portion. The cam is interposed between the connecting rod assembly and the crankpin. The driven portion is attached to the cam and is in a contacting relationship with the crankshaft drive portion through at least one contact interface. The contact interface is oriented at a non-zero angle to a radial reference originating from a centerline axis of the crankpin. The compressor includes structure for slidingly engaging and disengaging the drive portion with the driven portion through sliding movement of the drive portion relative to the driven portion along the contact interface.
The present invention further provides a method for compressing gas with a reciprocating piston compression device, including receiving a gas to be compressed into a cylinder of the compression device; rotating a crankshaft drive member in a first rotational direction; engaging a first surface of a camshaft driven member with a first surface of the crankshaft drive member through sliding movement between the drive and driven members; driving the cam in the first rotational direction; moving a piston operably connected to the cam assembly a first stroke distance; compressing the gas within the cylinder of the compression device; rotating the crankshaft drive member in a second rotational direction such that a second surface of a crankshaft drive member is rotated in a second rotational direction opposite the first rotational direction; engaging a second surface of the camshaft driven member with the second surface of the crankshaft drive member through sliding movement between the drive and driven members; driving the cam in the second rotational direction; and moving the piston operably connected to the cam assembly a second stroke distance.